1. Field of the Invention
The present invention relates to a method of growing carbon nanotubes, and more particularly to a method of horizontally growing carbon nanotubes, in which the carbon nanotubes can be selectively grown in a horizontal direction at specific locations of a substrate having a catalyst formed thereat, so that the method can be usefully utilized in fabricating nano-devices.
Also, the present invention relates to a method of horizontally growing carbon nanotubes, in which catalysts are formed in a shape of nanodots or nanowires at desired specific locations, so that the carbon nanotubes are selectively grown at specific locations, thereby the method can be usefully utilized in fabricating nano-devices.
Furthermore, the present invention relates to a field effect transistor, in which carbon nanotubes are grown in a horizontal direction to form a carbon nanotube bridge achieving a field effect transistor (FET), and in which catalysts in contact with a source and a drain, between which a carbon nanotube bridge is formed, are magnetized in a desired direction, so as to simultaneously achieve both a spin valve and a single electron transistor (SET).
2. Description of the Related Art
A carbon nanotube has a construction of one-dimensional quantum wire and has good mechanical and chemical characteristics. Also, it has been known that the carbon nanotube reveals very interesting electric characteristics such as the phenomenon of quantum transport. Further, much attention has been paid to the carbon nanotube as a new material, since it has newly discovered special characteristics, in addition to the above characteristics.
In order to utilize the superior characteristics of the material, a re-executable process of fabricating the carbon nanotube has to be preceded. However, in the existing process, after the carbon nanotubes are fabricated, they are individually handled one by one to be located at a desired position. Therefore, it is difficult to apply the existing process, in which the grown carbon nanotubes are located at desired positions in xe2x80x9can individual handling modexe2x80x9d, to an electronic element or a highly-integrated element, and many researches and developments are now being conducted in order to overcome this problem.
Further, in the vertical growth method, which is an existing method of synthesizing the carbon nanotubes, carbon nanotubes 6 (see FIG. 1) are grown in the vertical direction in a shape of a well-arranged barley field on a substrate 2, on which a pattern of catalyst is formed. Regarding the vertical growth method, a large quantity of report already exists.
However, in order to utilize the carbon nanotube as a nano-device having a new function, a technique capable of selectively growing the carbon nanotubes in the horizontal direction at specific positions is more useful and more highly required than the vertical growth technique, in a viewpoint of appliance.
The first report, which illustrates that carbon nanotubes can be horizontally grown between patterned metals to be connected with each other, was made by Hong Jie Die as shown in FIG. 2 (see Nature, vol. 395, page 878). FIG. 2 is a view for schematically showing the method of horizontally growing carbon nanotubes reported by Hong Jie Die. However, FIG. 2 apparently shows that a great many carbon nanotubes are grown not only in the horizontal direction but also in the vertical direction. This is because the carbon nanotubes are grown from surfaces of catalyst metal and moreover are randomly grown at all exposed surfaces of the catalyst.
In addition, since an effect of giant magneto resistance (GMR) was discovered in a multi-layer film comprising magnetic metal and non- magnetic metal in 1988, a research about a magnetic metal thin film is being widely conducted around the world. Moreover, since electrons exist in a spin-polarized state in the magnetic metal, polarized spin current can be generated by utilizing this characteristic. Therefore, a great effort has been made to understand and to develop the spin electronics (spintronics) or the magneto electronics by utilizing the degree of freedom of spin which is an important inherent characteristic of the electron.
Recently, such phenomena as tunneling magneto resistance (TMR) and giant magneto resistance (GMR) discovered in the magnetic multi-layer film system of nano-structure have already been applied in a magneto resistance (MR) magnetic head element and placed in a hard disc drive (HDD) of a computer to be commercialized.
In this case, TMR means a phenomenon, in which the tunneling current changes according to the relative magnetized direction of a ferromagnetic material in a junction having a construction of ferromagnet/dielectric (semiconductor)/ferromagnet, and which has a larger magnetic resistance ratio and a larger field sensitivity than other magnetic resistance, so that a research for utilizing it in a material for magnetic random access memory (MRAM) or magnetic resistance head of next generation has been actively performed. However, a re-executable formation of dielectric layer and reduction of junction resistance become serious problems.
Currently, a large number of scientists in the field of magnetic application are actively conducting researches in manufacturing MRAMS, utilizing a magnetic tunneling junction (MTJ) and a spin valve showing the phenomenon of magnetic resistance in the low magnetic field.
Accordingly, the present invention has been made in an effort to solve the aforementioned problems, and it is an object of the present invention to provide a method of horizontally growing carbon nanotubes, in which the carbon nanotubes can be selectively grown in a horizontal direction at specific locations of a substrate having catalyst formed thereat, so that the method can be usefully utilized in fabricating nano-devices.
Still, it is another object of the present invention to provide a method of horizontally growing carbon nanotubes, in which catalysts are formed in a shape of nanodots or nanowires at desired specific locations, so that the carbon nanotubes are selectively grown at specific locations, so that the method can be usefully utilized in fabricating nano-devices.
Still, it is another object of the present invention to provide a field effect transistor, in which carbon nanotubes are grown in a horizontal direction to form a carbon nanotube bridge, so as to achieve a field effect transistor (FET), and in which catalysts in contact with a source and a drain, between which a carbon nanotube bridge is formed, are magnetized in a desired direction, so as to simultaneously achieve both a spin valve and a single electron transistor (SET).
In accordance with one aspect, the present invention provides a method of horizontally growing carbon nanotubes, the method comprising the steps of: (a) forming a predetermined catalyst pattern on a first substrate; (b) forming a vertical growth preventing layer on the first substrate, which prevents carbon nanotubes from growing in a vertical direction; (c) forming apertures through the vertical growth preventing layer and the first substrate to expose the catalyst pattern through the apertures; and (d) synthesizing carbon nanotubes at exposed surfaces of the catalyst pattern, so as to grow the carbon nanotubes in the horizontal direction.
In this case, the apertures formed in the step c are of a hole-type, in which the apertures extend entirely through the vertical growth preventing layer and the first substrate, or a well-type, in which the first substrate is partially etched, so that the apertures extend through the vertical growth preventing layer and a portion of the first substrate.
In accordance with another aspect, the present invention provides a method of horizontally growing carbon nanotubes, the method comprising the steps of: (i) forming masks at predetermined locations on a first substrate; (j) forming a catalyst pattern on the first substrate and the masks formed on the first substrate; (k) forming a vertical growth preventing layer on the first substrate, which prevents the carbon nanotubes from growing in a vertical direction; (l) eliminating the masks from the vertical growth preventing layer and the first substrate, so as to form apertures and expose the catalyst pattern; and (m) synthesizing the carbon nanotubes at exposed locations of the catalyst pattern, so as to grow the carbon nanotubes in the horizontal direction.
In accordance with another aspect, the present invention provides a method of horizontally growing carbon nanotubes, the method comprising the steps of: forming a catalyst pattern in a predetermined two-dimensional arrangement on a first substrate; fabricating a second substrate for preventing vertical growth of the carbon nanotubes having holes in a predetermined arrangement; placing the second substrate for preventing vertical growth of the carbon nanotubes over the first substrate having the catalyst pattern with a predetermined gap; and synthesizing the carbon nanotubes at the catalyst pattern, so as to horizontally grow the carbon nanotubes.
In accordance with another aspect, the present invention also provides a method of horizontally growing carbon nanotubes, the method comprising the steps of: forming a catalyst in a shape of nanodots or nanowires on a substrate; patterning a growth preventing layer on the catalyst in the shape of nanodots or nanowires, so as to prevent the nanodots or nanowires from growing in a vertical direction; and selectively growing the carbon nanotubes in a horizontal direction at the nanodots or nanowires.
In this case, the catalyst in the shape of the nanodots or nanowires are patterned by an imprint method or a self-assembly method.
Further, the growth preventing layer may be formed of an insulator film made from a compound selected from the group consisting of silicon nitride (SiN) and silicon oxide (Sio2), or may be formed from a metal selected from the group consisting of Palladium (Pd), Niobium (Nb), and Molybdenum (Mo).
In accordance with another aspect, the present invention also provides a method of horizontally growing carbon nanotubes, the method comprising the steps of: forming catalysts in a shape of nanowires on a substrate; forming a growth preventing layer on the catalysts having the shape of nanowires by a semiconductor process including a lithography process, the growth preventing layer being spaced from the substrate with a predetermined gap; eliminating a portion of the catalysts having the shape of nanowires in an area at which the growth preventing layer is not formed, by means of a wet etching; and growing the carbon nanotubes in a horizontal direction between the catalysts formed under the growth preventing layer spaced from the substrate with a predetermined gap, by means of a chemical vapor deposition method.
Furthermore, in accordance with another aspect, the present invention also provides a field effect transistor comprising a source, a drain, and a carbon nanotube bridge between the source and the drain, the carbon nanotube bridge being formed by carbon nanotubes grown in a horizontal direction between the source and the drain, so that the field effect transistor can control a flow of electrons.
In this case, the carbon nanotube bridge formed between the source and the drain comprises carbon nanotubes having a characteristic of semiconductor.
Moreover, on the carbon nanotube bridge formed between the source and the drain, a plurality of gate carbon nanotubes are formed intersecting the carbon nanotube bridge between the source and the drain at, so as to produce an energy barrier to form a quantum point and to control the flow of the electric current.
Also, the quantum point has a size, which is controlled by using a common terminal, when the gate carbon nanotube bridges form gates.
Furthermore, the field effect transistor also comprises first and second wires, through which electric current can pass, and which are provided on the source and the drain, so as to magnetize catalysts being in contact with the source and the drain in a desired direction. The first wire disposed on the source and the second wire disposed on the drain are arranged in parallel with each other.